In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Typical block and sleeve assemblies have a block body with a bore therethrough from a front face to a rear face. A shaft of a tool pick is placed into the bore, either directly or with an intermediate sleeve. The tool pick has a shoulder that, in some instances, contacts the front face of the block. When present, the tool pick shoulder contacts the front face of the sleeve. Examples of blocks and/or block and sleeve assemblies are disclosed in U.S. Pat. No. 7,097,257; U.S. Pat. No. 7,234,782; U.S. Pat. No. 5,251,964; DE 4 204 542; DE 196 30 653; and DE 198 21 147, the entire contents of each are incorporated herein by reference.
Existing holder systems are prone to failure due to the excessive wear from repetitive impact of the pick shoulder against the block or sleeve face. These impacts cause deformation of the block or sleeve face. The deformation is in the form of a depression or indentation in the face, which results in more axial movement of the pick. As the axial movement increases, the deformation is accelerated. When the movement of the pick is too great, the block or sleeve must be replaced.
Another common wear issue on existing holder systems is frictional wear. As picks cut, abrasive fines that become trapped between their shoulders and the block or sleeve face erode the surface of the holder. This also shortens the life of the holder system.
U.S. Pat. No. 6,585,327 discloses a carbide ring that extends into the bore of a block or sleeve. As the pick strikes the material being cut, the pick shank is driven against the wall of the carbide ring. Cemented carbide has excellent compressive strength but weak tensile strength. When a shank is repeatedly driven into the wall of the carbide ring, it creates tensile loading that cause the carbide ring to fracture. Subsequent fractures result in the deterioration of the ring, rendering it ineffective.